***Useful Information for Apprentices***

[amberleaf]

“ General Health and Safety at Work “

Question 1.1
What do the letters CDM stand for ?
A: Control of Demolition and Management Regulations
B: Control of Dangerous Materials Regulations
C: Construction (Demolition Management) Regulations
D: Construction (Design and Management Regulations ) Answer: D )
Question 1.2
Identify one method of enforcing regulations that are
available to the Health and Safety Executive:
A: Health Notice
B: Improvement Notice
C: Obstruction Notice
D: Increasing insurance premiums
Answer: B Improvement notices require action to achieve standards which meet health and safety law :
Question 1.3
What happens if a Prohibition Notice is issued by an
Inspector of the local authority or the HSE ?
A: The work in hand can be completed, but no new work started
B: The work can continue if adequate safety precautions are put in place
C: The work that is subject to the notice must cease
D: The work can continue, provided a risk assessment is carried out,
Answer: C The work covered by a prohibition notice must cease until the identified danger is removed.
Question 1.4
Health and Safety Executive Inspector can ?
A: Only visit if they have made an appointment
B: Visit at any time
C: Only visit if accompanied by the principal contractor
D: Only visit to interview the site manager
Answer: B Inspectors have a range of powers, including the right to visit premises at any time.
Question 1.5
A Prohibition Notice means:
A: When you finish the work you must not start again
B: The work must stop immediately
C: Work is to stop for that day only
D: Work may continue until the end of the day
Answer: B The work activity covered by the prohibition notice must cease, until the identified danger is removed ,
Question 1.6
In what circumstances can an HSE Improvement Notice be issued ?
A: If there is a breach of legal requirements
B: By warrant through the police
C: Only between Monday and Friday on site
Answer: A Improvement notices require action to achieve standards which meet health and safety law .
Question 1.7
What is an “Improvement Notice”?
A: A notice issued by the site principal contractor to tidy up the site
B: A notice from the client to the principal contractor to speed up the work
C: A notice issued by a Building Control Officer to deepen foundations
D: A notice issued by an HSE/local authority Inspector to enforce compliance with health
Answer: D Improvement notices require action to achieve standards which meet health and safety law .
Question 1.8
If a Health and Safety Executive Inspector issues a“ Prohibition Notice”, this means that:
A: the Site Manager can choose whether or not to ignore the notice
B: specific work activities, highlighted on the notice, must stop
C: the HSE must supervise the work covered by the notice
D: the HSE must supervise all work from then on
Answer: B Prohibition notices are intended to Stop activities which can cause serious injury.
Question 1.9
Which one of the following items of information will you find on the Approved Health and Safety Law poster?
A: Details of emergency escape routes
B: The location of the local HSE office
C: The location of all fire extinguishers
D: The identity of the first aiders
Answer: B The poster also lists the persons with health and safety responsibilities, but not first aiders.
Question 1.10
Who is responsible for signing a Company Safety Policy ?
A: Site Manager
B: Company Safety Officer
C: Company Secretary
D: Managing Director
Answer: D The Health and Safety at Work Act requires the most senior member of management to sign the health and safety policy
statement.

Question 1.11
Which one of the following must be in a company’s written Health and Safety Policy:
A: Aims and objectives of the company
B: Organisation and arrangements in force for carrying out the health and safety policy
C: Name of the Health and Safety Adviser
D: Company Director’s home address
Answer: B This requirement appears in the Health and Safety at Work Act.
Question 1.12
Employers have to produce a written Health and Safety Policy statement when:
A: A contract commences
B: They employ five people or more
C: The safety representative requests it
D: The HSE notifies them
Answer: B This is a specific requirement of the Health and Safety at Work Act.
Question 1.13
Companies employing five or more people must have a written Health and Safety Policy because:
A: The principal contractor gives them work on site
B: The HSAWA 1974 requires it
C: The Social Security Act requires it
D: The trade unions require it
Answer: B
Question 1.14
What do the letters HSC stand for ?
A: Health and Safety Contract
B: Health and Safety Consultant
C: Health and Safety Conditions
D: Health and Safety Commission Answer: D
Question 1.15
Which ONE of the following statements is correct ? The Health and Safety Executive is:
A: a prosecuting authority
B: an enforcing authority
C: a statutory provisions authority
Answer: B The Health and Safety Executive enforces health and safety legislation.
Question 1.16
The Health and Safety at Work Act requires employers to provide what for their employees?
A: Adequate rest periods
B: Payment for work done
C: A safe place of work
D: Suitable transport to work
Answer: C This is a specific requirement of Section 2 of the Health and Safety at Work Act.
Question 1.17
The Health and Safety at Work Act 1974 and any regulations made under the Act are:
A: Not compulsory, but should be complied with if convenient
B: Advisory to companies and individuals
C: Practical advice for the employer to follow
D: Legally binding Answer: D
Question 1.18
Under the Health and Safety at Work Act 1974, which of the following have a duty to work safely?
A: Employees only
B: The general public
C: Employers only
D: All people at work
Answer: D Employers, employees and the self-employed all have a duty to work safely under the Act.
Question 1.19
What is the MAXIMUM penalty that a Higher Court, can currently impose for a breach of the Health and Safety at Work Act?
A: £20,000 fine and two years imprisonment
B: £15,000 fine and three years imprisonment
C: £1,000 fine and six months imprisonment
D: Unlimited fine and two years imprisonment
Answer: D A Lower Court can impose a fine of up to £20,000 and/or up to six months imprisonment for certain offences. The potential fine in a Higher Court, however, is unlimited and the term of imprisonment can be up to 2 years.
Question 1.20
What do the letters ACoP stand for ?
A: Accepted Code of Provisions
B: Approved Condition of Practice
C: Approved Code of Practice
D: Accepted Code of Practice
Answer: C An ACOP is a code of practice approved by the Health and Safety Commission.

Question 1.21
Where should you look for Official advice on health and safety matters?
A: A set of health and safety guidelines provided by suppliers
B: The health and safety rules as laid down by the employer
C: Guidance issued by the Health and Safety Executive
D: A professionally approved guide book on regulations
Answer: C The HSE is the UK enforcing body and its guidance can be regarded as ‘official’
Question 1.22
Regulations that govern health and safety on construction sites:
A: apply only to inexperienced workers
B: do not apply during ’out of hours’ working
C: apply only to large companies
D: are mandatory ( that is, compulsory )
Answer: D The requirements of health and safety law are mandatory, and failure to follow them can lead to prosecutions.
Question 1.23
Which of the following statements is correct ?
A: The duty for health and safety falls only on the employer
B: All employees must take reasonable care, not only to protect themselves but also their colleagues
C: Employees have no responsibility for Health and Safety on site
D: Only the client is responsible for safety on site
Answer: B The responsibility for management of Health and Safety Act at Work rests with the employer
Question 1.25
Which of the following is correct for risk assessment?
A: It is a good idea but not essential
B: Only required to be done for hazardous work
C: Must always be done
D: Only required on major jobs
Answer: C There is a legal requirement for all work to be suitably risk assessed.
Question 1.26
In the context of a risk assessment, what do you understand by the term risk?
A: An unsafe act or condition
B: Something with the potential to cause injury
C: Any work activity that can be described as dangerous
D: The likelihood that harm from a particular hazard will occur
Answer: D Hazard and risk are not the same. Risk reflects the chance of being harmed by a hazard
Question 1.27
Who would you expect to carry out a risk assessment on your working site?
A: The site planning supervisor
B: A visiting HSE Inspector
C: The construction project designer
D: A competent person
Answer: D A risk assessment must be conducted by a 'competent person’.
Question 1.28
What is a HAZARD ?
A: Where an accident is likely to happen
B: An accident waiting to happen
C: Something with the potential to cause harm
D: The likelihood of something going wrong
Answer: C Examples of hazards include: a drum of acid, breeze blocks on an elevated plank; cables running across a floor.
Question 1.29
What must be done before any work begins ?
A: Emergency plan
B: Assessment of risk
C: Soil assessment
D: Geological survey
Answer: B This is a legal requirement of the Management of Health and Safety at Work Regulations.
Question 1.30
Complete the following sentence: A risk assessment
A: is a piece of paper required by law
B: prevents accidents
C: is a means of analysing what might go wrong
D: isn’t particularly useful
Answer: C Risk assessment involves a careful review of what can cause harm and the practical measures to be taken to reduce the risk of harm.

 

[amberleaf]

method when installing cable on insulation ?

Reference methods 100 and 101 refer to twin & earth (T/E) cable installed within various thickness of insulation. What reference method should I use when cable is installed on top of any insulation ?

Regulation 523.7 of BS-7671 requires that, where a cable is to be run in a space to which thermal insulation is likely to be provided, the cable is - wherever practicable - to be fixed in a position where it will not be covered by the thermal insulation.

the cable would appear to be in contact with thermal insulation on one side only. Therefore, if there is free air on the remaining sides of the cable, reference method 'C' for either Table 4D2A or Table 4D5 would be appropriate.

BS5803-5:1985
Thermal insulation for use in pitched roof spaces in dwellings. Specification for installation of man-made mineral fibre and cellulose fibre insulation

Thermal insulating materials, Roof spaces, Pitched roofs, Domestic facilities, Man-made fibres, Mineral fibres, Cellulose, Fibres, Installation, Sheet materials, Pellets, Beads, Particulate materials, Thermal insulation, Water storage cisterns, Pipes, Ven
Cross references :
BS 874, BS 3533, BS 3589, BS 5250, BS 5422, BS 5803art 1, BS 5803art 2, BS 5803art 3, BS 7671, PD 6501art 1

Loft Insulating Materials
Mineral fibre or fibreglass matting is usually available in rolls 400mm (16in) wide. Thicknesses range from 100mm (4 in) to 200mm (8 in). In the UK, the total thickness of insulation should be at least 200mm (8in), the thinner insulation material available allow for old, thinner loft insulation to be overlaid to achieve the 200mm. Roll insulation

Sheep’s Wool insulation is a general purpose natural wool fibre product designed for use in loft, rafter, internal wall and inter-floor applications. It is specifically constructed to match and surpass the Part L Building Standards with reference to Thermal, Fire, Mould Resistance and Structural performance.

 

[amberleaf]

COLD BENDING 20-25MM CONDUIT

This may be carried out on all conduit sizes up to25mm in diameter using the correct size and gauge of bending spring. It should be noted that the heavy gauge spring is colour banded green and the light gauge spring colour banded white near the tip of the spring. These springs are not interchangeable under any circumstances. Make sure they are not damaged in any way as this can cause the conduit to kink and fracture making removal of the spring difficult.(In cold weather the Conduit should be warmed by rubbing with a rag or some other suitable means before bending.)

To bend the conduit insert the spring to the desired position, grip the conduit on either side of the
bend and bring slowly together to form the bend. The bend should be made more acute than necessary because of the tendency of the PVC-U to ‘recover’ after bending. To remove the spring twist in an anti-clockwise direction which will reduce its in an anti-clockwise direction which will reduce its diameter. At the same time turn the conduit in a
clockwise direction gently pulling the spring and conduit apart. If the spring fails to release during this operation do not pull too hard otherwise damage to the spring may occur. Repeat the removal procedure turning the spring again in an
anti-clockwise direction and rotating the conduit clockwise slowly pulling them apart. The conduit
should then be fastened into position to prevent further ‘recovering’ of the bend.

HOT BENDING

This should be carried out on all conduit above25mm diameter using the correct size and gauge of
bending spring. Insert the bending spring into the conduit as previously described, gently heating the
conduit with a hot air torch, hot water or by other suitable means, with care being taken to avoid the
direct application of a flame to the conduit. When the conduit is in a pliable state, slowly bend around a suitable former, holding in position for about one minute until set when the bending spring may then be removed by twisting in an anticlockwise direction and gently withdrawing from the conduit. If the conduit is bent too fast or, particularly in the
case of light gauge across the knee, there is a risk of damage to both the conduit and spring. Similarly
once the bend has been made it should not be forced backwards but allowed to recover naturally.

JOINTS AND COUPLERS

To accommodate for thermal movement due to temperature change (Materials Data) on surface installations, it is recommended that expansion
couplings be used at a maximum distance of 6m intervals. Where high ambient temperatures or frequent variations in temperature are likely to occur this distance should be reduced. Expansion couplers are installed with the →→ short side coated with solvent cement ←← and the coupler pushed firmly over the conduit down to the shoulder. The slip side coated inside with lubricant sealant receives the conduit to a midpoint to the nib. This will then permit expansion or contraction providing the conduit is free to move in the saddles.

Conduit fittings are installed in the system using solvent cement (MSC20) for permanent installations and lubricant sealant (MSC1) where the installation is subject to frequent changes.

Straight runs exceeding 3 metres, or runs of any
length incorporating bends or sets. The term ‘bend’ signifies a British Standard 90º bend and one double set is equivalent to one bend.

Conduit / Following cable factors :

O.S.G ( table 5C ) 16 for 1mm2 , 30 for 2.5mm2 & 58 for 6mm2
Cf : ( 8 x 16 ) + ( 4 x 30 ) + ( 2 x 58 ) = 128 + 120 + 116 = 364

the term “ bend “ means a right angle bend or left angle or double set ,

O.S.G ( table 5D ) gives a conduit factor for 20mm conduit 6m long with double set as 233 ,
Which is less than 364 and thus to small . The next size has a conduit factor of 422 which will be acceptable since it is larger than 364 .

The correct conduit size is 25mm diameter ,

O.S.G ( table 5D ) 10m long Straight 25mm conduit has a factor of 442 . This is too small , so the next size , with a factor of 783 must be used ,
The correct conduit size is 32mm diameter ,

Example :
1.5mm2 Straight length of conduit from a Consumers Unit encloses ten 1.5mm2 & four 2.5mm2 Solid ↔ Conductor P.v.c
Insulated cables , Calculate a suitable Conduit size ,

From O.S.G ( table 5A ) which is for short straight runs of conduit ) total cable factor will be :
1.5mm2 ↔ 10 x 27 + 2.5mm2 ↔ 4 x 39 = 426

From O.S.G ( table 5B ) 20mm diameter conduit with a factor of 460 will be necessary ,

Example :

A length of trunking is to carry eighteen 10mm2 , sixteen 6mm2 , twelve 4mm2 , and ten 2.5mm2 Stranded single P.v.c
Insulated cables , Calculate a suitable trunking size , O.S.G ( table 5E )
18 x 10mm2 at 36.3 = 18 x 36.3 = 653.4
16 x 6mm2 at 22.9 = 16 x 22.9 = 366.4
12 x 4mm2 at 15.2 =12 x 15.2 = 182.4
10 x 2.5mm2 at 11.4 = 10 x 11.4 = 114.0
Total cable factor = 1316.2

From the trunking factor O.S.G ( table 5F )
Two stranded trunking sizes have factors slightly greater than the cable factor , and either could be used ,
They are ( 75mm x 50mm at 1555 ) & ( 100mm x 38mm at 1542 )

CAPACITY EXAMPLE : 5C

Number of cables for a 3.0 metre run with three bends
CONDUIT 20mm dia.
CABLE SOLID 2.5mm2 ( 3 qty )
CABLE STRANDED 4.0mm2 (2 qty )
Term total – ( 30+30+30 )+( 43+43 ) = 176

Note-: It is recommended that a 32 TPI hacksaw blade be used for cutting steel trunking.

Earthing of Steel Trunking

A trunking installation must be earthed. Earth continuity is ensured by the proper tightening of all bolts used throughout the system. Some manufactures recommend that earth continuity be completed by fixing a copper or aluminium strap across all joints. It is more important that all the bolts involved in the system are tightened. It is not unusual to find that copper or aluminium straps are used, but are left loose, resulting in poor earth continuity.

Eddy Currents in Steel Conduit

Metal conduits in which a.c. circuit wiring is installed MUST contain all the current carrying conductors of each circuit in the same conduit, to eliminate the possibility of induced eddy currents. Eddy currents could result in the metal conduit and cables becoming hot.

Some Advantages of Steel Conduit
• Affords cables good mechanical protection
• Permits easy rewiring
• Minimises fire risks.
• Can be utilized as the Circuit Protective Conductor. ( CPC )

Cable Capacity of Steel Conduit ( Space Factor )

Having determined the correct number and cross-sectional area of cables for a given load it is necessary to select the size of conduit that will accomodate them.
If a greater number of cables are installed in the conduit, over-heating, insulation damage and fire may result. As a general rule the number of cables drawn into a conduit should not be such as to cause damage to either the cables or the conduit during the installation.

Termination of Steel Conduit to Enclosures

Two methods of terminating steel conduit are commonly used.
• The coupling and male bush method, (Usually used and preferred)
• The locknut and female bush method, (Used where space is tight)

Jointing Steel Conduit

Where two lengths of conduit are to be joined a plain coupling is used. To ensure good electrical continuity and maximum mechanical strength the tube ends must tighten inside the coupling (Max gap 2 mm) Care must be exercised to do this without leaving threads outside the coupling.
Where neither tube can be turned it is necessary to resort to the technique known as the “running coupling” , After tightening up the lockring the exposed thread must be painted to prevent corrosion.
Expansion of PVC Conduit
Expansion couplings should be used for surface installations at a recommended maximum of 4 metre intervals.
Where frequent variations in ambient temperature are likely to occur this distance must be greatly reduced.

Advantages of PVC Conduit
• Lightweight and easy to handle
• Easy to cut and deburr
• Simple to form and bend
• Does not require painting
• Minimal condensation due to low thermal conductivity in wall of conduit.
• Speed of installation
• Excellent electrical and fire resistant properties

Disadvantages of PVC Conduit

• Care must be taken when glueing joints to avoid forming a barrier across the inside of the conduit.
• If insufficent adhesive is used the joints may not be waterproof.
• PVC expands about 5 times as much as steel and this expansion must be allowed for.
• PVC does not offer the same level of mechanical protection as steel.
• A separate Circuit Protective Conductor must be run inside the conduit.

 

[amberleaf]

Ways of assessing Knowledge Evidence:
Questioning
Both verbal and written questioning gives the teacher/tutor the opportunity to gauge the learner’s understanding and allows them to demonstrate their underpinning knowledge. Questioning can be done during feedback sessions and can be used to check whether learners can understand their mistakes when errors are pointed out or to explore in greater depth a situation which has arisen.
• Oral questions
Oral questioning is used to check a learner’s underpinning knowledge of the subject. The learner can be asked questions about a subject which has just taken place or more general questions to check on their knowledge about other topics in which they are involved. If the answers to the oral questioning are to provide final portfolio evidence, concise but clear notes should be made at the time by the assessor. These notes should be signed and dated by the learner and by the assessor for verification purposes.
• Written questions
Written questions could be set in the contexts of task sheets, short tests or homework and can take several forms from short to extended answers. They are a valuable assessment tool to check a learner’s underpinning knowledge as it gives the teacher/tutor the opportunity to ask more searching questions and the learner the opportunity to think about their answers and to do some research if necessary. Once the answers have been assessed, the learner and their assessor have some tangible evidence which can form a basis for discussion and there will be a record of the answers in the portfolio.
• Pre-set questions
These could be set by the assessor as homework, or given under test conditions. In some circumstances, they could also be examination questions set by the Awarding Body. In this case, all learners doing the qualification are being given the same sets of questions in the interests of fairness and standardising assessment practices. A bank of questions may be produced which are used for assessment purposes by all assessors for a standard approach.
• Assessor devised questions
These would generally be set by the teacher/tutor. Some sets of questions may need to be specifically devised to test certain required skills. Other questions can be devised to be used as a learning tool for the learner and an assessment tool for the teacher/tutor. They are valuable in that they allow the teacher/tutor to be responsive to the particular conditions under which the learner is working.

An ammeter inserted in the circuit will record a PLUS and MINUS READING. Which means the current is flowing in the opposite direction.

In most cases many cycles of the waveform occur in one second and the number of
cycles which occur per second is known as the FREQUENCY – Symbol ( f ). Frequency is measured in HERTZ - (Hz).

Time ( mS ) : there are five cycles occurring in one second and hence :- Frequency ( f ) = 5 Hz
Relationship between frequency and period (time):-
( a ) f = 1 – T Hz or ( b ) T – 1 – f sec

Where T is the PERIOD (i.e. the time taken to complete one waveform )

Examples :
1. A waveform has a frequency of 5 Hz, calculate the period of the waveform.
T = 1 – f = 1 – 5 = 0.2 sec
(This means 1 waveform will be traced every 0.2 seconds)
2. If the period of an AC waveform is 5milli seconds , find the frequency
5 milli seconds = 0.0005 seconds
f = 1 – T = 1 ÷ 0.0005 = 200Hz

Exercise :
1. Given the following frequencies, calculate the period of the waveform.
(a) f = 100Hz
(b) f = 5Hz
(c) f = 20Hz
(d) f = 100Hz
(e) f = 1Hz

2. Given the following periods of each cycle calculate the frequency of the waveforms.
(a) T = 0.05 seconds
(b) T = 2 seconds
(c) T = 25 milliseconds
(d) T = 125 milliseconds
(e) T = 5 milliseconds

Power Dissipation :

All components have resistance so when a current flows through them power is dissipated in most cases in the form of heat. It is something to be aware of in the selection of components to be used in a circuit that the power ratings are not exceeded, examples are bulbs and resistors.

Example 1
Find the power dissipated by the bulb ( Resistance of bulb = 100 ohms )
To find the power dissipated in the bulb which has a resistance of 100Ω
If the formula Power = I x V watts is to be used the following data must be known: current flowing through the bulb and voltage across the bulb.
As the 200 Ohms resistor and the lamp are in series then :
R t = 200 + 100 = 300Ω
So now having one voltage and one resistance the current flowing in the circuit can be calculated :
I = V – Rt = 9v ÷ 300 = 0.03 Amps
The voltage across the bulb can be found:
V (bulb) = I x R where R = the resistance bulb and I is the current
Vd = 0.03 x 100 = 3volts
We now have values for both the current through the bulb and the voltage across it.
P = I x V = 0 .03 x 3 = 0 .09W or 90mW.
The power could also be calculated using the formula : Power = V2 – R = 9 ÷ 100 = 0.09 watts

Example 2
In the circuit shown calculate the power dissipated in the 3Ω resistor.
18V / R1 = 4Ω R2 = 6Ω R3 = 3Ω
The first step is to find the total résistance of the circuit.
R2 and R3 are in parallel and this parallel arrangement is in series with R1
To calculate the parallel pair R2 // R3 ( let equivalent resistance = Rv )
Rv = R2 x R3 = 6 x 3 = 18
…….R2 + R3 ….. 6 + 3 ….. 9 = 2 Ω

Circuit now reads R1 and R2 in series.
18V / R1 = 4Ω Rv = 2Ω : R total = R1 + Rv = 4 + 2 = 6Ω

From having one voltage and one resistance the current flowing in the circuit can be found:
18V R total = 6Ω ( I = V – R total = 18 ÷ 6 = 3 Amps

Knowing there is 3Amps flowing in the circuit we can now calculate the voltage across the two resistors in parallel. Remember that their effective resistance is 2Ω

Voltage across parallel block: I x Rv = 2 x 3 = 6volts 18V R1 =4 Ω R2 = 6 Ω R3 = 3Ω V = 6V : Voltage = 6V Résistance = 3 Ω Power dissipated by the resistor : Power = V2 – R = 6 x 6 – 3 = 12 Watts

Exercises :
(a) In the circuit shown the motor has an internal resistance of 10Ω Find the power developed by the motor. ( 20V )
(b) Calculate the power dissipated in the 12Ω resistor. ( 54V / 6Ω 120Ω )
(c) The bulb shown has a filament resistance of 12 ohms. Calculate the output power. ( 45V / 6Ω 120Ω ulb )
(d) In the circuit shown all the bulbs have a resistance of 10Ω. Find the output power B3 : ( 30V / B1 / B2 / B3 )

 

[amberleaf]

Ohms Law :

Power = V2 – R or R x I2 or V x I
Voltage = P – I or R x I or √ P x R
Resistance = V – I or V2 – P or P – I2
Current = P – V or V – R or √ P – R

1a) Three resistors are connected in series to a 240 V power supply. One of the resistors is rated at 10 Ω, one at 15 Ω, and the third is unknown. If the current in the circuit is measured to be 4 A, what is the total resistance of the circuit ? ( 60 Ω )

1b) What is the rating of the unknown resistor ? ( 35 Ω )

1c) What is the voltage drop across the unknown resistor ? ( 140 V )


2 ) Four resistors are hooked up in series to unknown power supply. The resistors are rated as follows; 5 Ω, 10 Ω, 20 Ω, and 25 Ω. If the voltage drop across the 10 Ω resistor is measured to be 60 V, what is the rating of the power supply ? ( hint: first find the current in the circuit )( 360 V )

V . R1.R2.R3 ,

V/1 . 120 V. R1 5 Ω . I1 24 A
V/2 . 120 V. R2 10 Ω . I2 12 A
V/3. 120 V. R3 25 Ω . I3 4. 8 A
V total 120V . R total 2.94 Ω . I total 40.8 A
Fill in the rest of the blanks if V total = 120V, R1 = 5 Ω, R2 = 10 Ω, and R3 = 25 Ω

* Ohm’s Law V I R =
(Voltage drop equals current times resistance.)
This is the main equation for electric circuits but it is often misused. In order to
calculate the voltage drop across a light bulb use the formula: V light bulb = I light bulb R light bulb
For the total current flowing out of the power source, you need the total resistance of the circuit and the total
Current : V . total = I total , R total ,

Power is the rate that energy is released. The units for power are Watts (W), which
equal Joules per second [W] = [J]/. Therefore, a 60 W light bulb releases 60 Joules energy every second

The equations used to calculate the power dissipated in a circuit is P. I V =

As with Ohm’s Law,
one must be careful not to mix apples with oranges. If you want the power of the entire circuit, then you multiply the total voltage of the power source by the total current coming out of the power source. If you want the power dissipated (i.e. released) by a light bulb, then you multiply
the voltage drop across the light bulb by the current going through that light bulb

 

[amberleaf]

Why measure earth loop impedance ?

Earth loop impedance testing is essential since if a live conductor is accidentally connected to an earth conductor in a faulty appliance or circuit, the resulting short-circuit current to earth can easily be high enough to cause electric shock or generate enough heat to start a fire. Normally, the fuse will blow or another circuit protection device will trip, but a
situation may arise where the actual short-circuit current in a faulty installation is of insufficient level and the protection device would thus take too long to activate. The delay can be disastrous for life and property. It is therefore necessary to know if the impedance of the path that any fault current would take is low enough to allow sufficient current to flow in the event of a fault and that any installed protective device will operate within a safe time limit.

Verifying protection by automatic supply disconnection :

fault loop testing falls under the category of ‘Verifying protection by automatic supply disconnection’.
This covers verification of the effectiveness of protective measures, and the test methods applied depend on the type of system. TT systems, for example, require measurement of the earth electrode resistance for exposed conductive- parts of the installation,
whereas IT systems use calculation or measurement of the first fault current. This application note looks specifically at TN systems, which require measurement of the fault loop impedance and verification of the characteristics of the associated protective device ( i.e. visual inspection of the nominal current setting for circuit-breakers, the current ratings and blow characteristics
for fuses and the correct functioning of RCDs ).

The earth loop impedance of each individual circuit from the point of use back to the incoming supply connection point should be measured.

A separate measurement of the external loop impedance of the installation can also be made at the incoming supply point or main distribution panel and this value will form part of the overall loop impedance from any part of the final circuit installation. Knowing the earth loop impedance, it is possible to calculate the value of the prospective fault current (PFC) at any point in an installation and to ensure that all installed protective devices are of an adequate rating to clear the potential fault current level.

Measuring earth loop impedance :

Since the AC impedance of a circuit may be different from its DC resistance particularly for circuits rated at over
100 A – the fault loop impedance is measured using the same frequency as the nominal mains frequency (50 Hz).
The earth loop impedance test measures the resistance of the path that a fault current would take between line and protective earth. This must be low enough to allow sufficient current to flow to trip a circuit protection device such as a fuse or miniature circuit breaker.

testers can be
used to carry out the test at a distribution board using the three separate test leads supplied, and at appliance
outlets using a dedicated lead fitted with a mains plug. A plug of the appropriate national standard is also

Determining the PFC is important to ensure that the capability of fuses and over-current circuit breakers are not exceeded.

Interpreting results and taking remedial action :

Remember that it is not sufficient just to carry out tests and record the results. Knowledge of Regulations– and of how to interpret results – is also required to ensure the installation’s safety characteristics are within the prescribed limits. An excessive earth loop impedance value should, for example, prompt an investigation into its cause. Remedial be carried out, and the installation action should then retested.

Multifunction Installation Testers have a loop impedance test function in addition to being able to measure
prospective short circuit current (PSC) and fault current (PFC).

Proper use of clamp meters in commercial and residential environments ?

Clamp meters in residential applications;

For residential electricians, clamps are a necessity to measure loads on individual branch circuits at the distribution panel.
While a spot check of current is often sufficient, sometimes it doesn’t provide the full picture as loads are switching on and off, going through cycles, etc. Voltage should be stable in an electrical system, but current can be very dynamic. peak or worst-case loading on To check the a circuit, use a clamp with a min/max function which is designed to catch high currents that exist for longer than 100 ms, or about eight cycles. These currents lead to intermittent overload conditions which can cause nuisance tripping of circuit breakers.
Take measurements on the load side of the circuit breaker load side of the circuit breaker or fuse. The breaker will open the circuit in the event of an accidental short circuit. This is especially important with any kind of direct-contact voltage measurement. Even though
clamp jaws are insulated and therefore have a level of protection that doesn’t exist with direct-contact voltage measurement, it’s still a good idea to be cautious. A common problem in residential electrical work is mapping outlets to breakers.
A clamp can be useful in identifying which circuit a particular outlet is on. First take a baseline reading, at the distribution panel, of the existing current on the circuit. Then put the clamp in min/max mode. Go to the outlet in question, plug in a load—a hair dryer is ideal—and turn it on for a second or two. Check the clamp to see if the max current reading has changed. A hair dryer will typically draw 5 A, so there should be a noticeable difference. If the reading is the same, you’ve got the wrong breaker.

Clamp meters in commercial environments :

Clamp meters are used at the panelboard to measure circuit loading on feeders as well as on branch circuits. Measurements on branch circuits should always be made at the load side of the breaker or fuse.
• Feeder cables should be checked for balance as well as loading: current on all three phases should be more
or less the same, to minimize the return current on the neutral.
• The neutral should also be checked for overloading. With harmonic loads, it’s possible for the neutral to be
carrying more current than a feeder—even if the feeders are balanced.
• Each branch circuit should also be checked for possible overloading.
• Finally the earth circuit should be checked. Ideally there should be no current on the earth,

Testing for leakage currents :

To check if there is leakage current on a branch circuit, put both the live and neutral wires in the jaws of the clamp. Any
current that is measured is leakage current, i.e., current returning on the earth circuit The supply and return currents
generate opposing magnetic fields. The currents should be equal (and opposite) and the opposing fields should cancel
each other out. If they don’t, that means that some current, called leakage current, is returning on another path, and
the only other available path is the earth. If you do detect a net current between the supply and return, consider the nature of the load and the circuit. A mis-wired circuit can have up to half of the total load current straying through the earth system. If the measured current is very high, you probably have a wiring problem. Leakage current may also be caused by leaky loads or poor insulation. Motors with worn windings or moisture in fixtures are common culprits. If you
suspect excessive leakage, a de-energized test using a megohm -meter will help evaluate the integrity of the circuit’s insulation and help identity if and where a problem exists.

Continuity :

Testing the continuity of protective conductors is normally carried out with an instrument being able to generate a no-load voltage in the
range 4 to 24 V (DC or AC) with a minimum current of 0.2 A. The most common continuity test is measuring the resistance of protective
conductors, which involves first confirming the continuity of all protective conductors in the installation, and then testing the main and supplementary equipotential bonding conductors. All circuit conductors in the final circuit are also tested. ( 612.2.1 ) ↔

As Continuity Testing Measures very Low Résistances ,
the resistance of the test leads must be compensated for. a time-saving Auto-Null feature that, by simply touching the test leads together and
pressing the zero button, measures and stores the test lead resistance,

 

[amberleaf]

Verifying protection by automatic supply disconnection :

Verification of the effectiveness of the measures for protection against indirect contact by automatic disconnection of supply depends on
the type of system. In summary, it is as follows:

• For TN systems: measurement of the fault loop impedance; and verification of the characteristics of the associated protective device
the associated protective device nominal current setting for circuit breakers, the current ratings for fuses and testing RCDs).

• For TT systems: measurement of the earth electrode resistance for exposed-conductive-parts of the installation; and verification of the
characteristics of the associated protective device (i.e. RCDs by visual inspection and by test).

• For IT systems: Calculation or measurement of the fault current.

Measurement of fault loop impedance :

Measurement of the fault loop impedance is carried out using the same frequency as the nominal frequency of the circuit (50 Hz). The
earth-loop impedance test measures the resistance of the path that a fault current would take between line and protective earth, which must be low
enough to allow sufficient current to flow to trip a circuit protection device such as a MCB (Miniature Circuit Breaker).

Functional test :

All assemblies, such as switchgear and control gear assemblies, drives, controls and interlocks, should be functionally tested to show that they
are properly mounted, adjusted and installed in accordance with the relevant requirements of the standard. Protective devices must be
functionally tested to check whether they are properly installed and adjusted.

Polarity test :

Where regulations forbid the installation of single-pole switching devices in the neutral conductor, a test of polarity must be made to
verify that all such devices are connected in the phase only. Incorrect polarity results in parts of an installation remaining connected
to a live phase conductor even when a single-pole switch is off, or an over-current protection device has tripped.

 

[amberleaf]

Where metal conduit is used as a protective conductor, its cross-sectional area shall be determined either by application of the formula of 543.1.4 , or Table 54.7

* AC motor :
A type of electric motor that runs on alternating current. AC motors are more commonly used in industry than DC motors but do not operate well at low speeds.
* alternating current :
Current that regularly reverses the direction of its flow in a repeating, cyclical pattern.
* armature :
The part of a motor or generator in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
* bearing :
A friction-reducing device that allows one moving part to glide past or rotate within another moving part.
* brush :
A device found inside a generator that is used only in pairs to transfer power from a rotating object. Brushes rest on the commutator of a DC motor.
* capacitor :
An electrical device that stores energy and releases it when needed. A capacitor gives a single-phase motor more torque but has a limited life.
* capacitor motor :
A single-phase motor with a running winding, starting winding, and a capacitor. Capacitor motors have more torque than other single-phase motors.
* capacitor start-and-run motor :
A type of capacitor motor that uses two capacitors, one for starting the motor, and one that remains in the circuit while the motor is running.
* capacitor-run motor :
A type of capacitor motor that has a capacitor and starting winding connected in series at all times.
* capacitor-start motor :
A single-phase motor with a capacitor. The capacitor gives the motor more starting torque.
* centrifugal switch :
A type of switch that operates using the centrifugal force created from the rotating shaft. The centrifugal switch activates and de-activates depending on the speed of the motor.
* direct current :
A current formed when electrons flow in one continuous direction.
* dual voltage motor :
A type of three-phase motor that operates on two voltage levels. Dual voltage motors allow the same motor to be used with two different power line voltages.
* electric motor :
A machine that converts electricity into mechanical energy or motion. An electric motor is a common power source for a mechanical system.
* efficiency losses :
A measure of the energy output versus the amount of input energy. The output energy is typically less than the input energy.
* electromagnetic induction :
The process in which current is induced in a magnetic field using a current-carrying coil. An AC generator produces a current through electromagnetic induction.
* field winding :
The conducting wire connected to the armature that energizes the pole pieces. Field windings are connected in series or parallel.
* generator :
A device that converts mechanical energy into electrical energy by magnetic induction.
* induction motor :
A type of AC motor that uses electrical current to induce rotation in the coils.
* magnet :
A device or object that attracts iron and produces a magnetic field.
* magnetic flux :
The area in and around a magnet that exhibits the powers of attraction and repulsion. Rotating an armature through lines of magnetic flux induces AC.
* motor nameplate :
A plate attached to a motor that displays all of the motor's information
* output shaft :
The rotating part on the AC motor that holds the rotor and allows it to turn.
* phase displacement :
The separation of the three phases in a three-phase motor. The windings are spaced 120º apart.
* reactance :
The resistance to the flow of alternating current due to inductance.
* resistance :
The opposition to current flow. Electricity flows in the path of least resistance.
* rotor :
The rotating part of a motor.
* running winding :
Heavy, insulated copper wire in a single-phase motor that receives the current for running the motor. The running winding remains connected when the starting winding is disconnected.
* secondary winding :
The second winding that current passes through in a transformer. The secondary winding contains fewer, but thicker wires that are wrapped into a coil.
* shaded-pole motor :
A single-phase motor that is 1/20 HP or less and is used in devices requiring low torque.

* sine wave :
The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
* single voltage motor :
A type of three-phase motor that operates on only one voltage level. Single voltage motors are limited to having the same voltage as the power source.
* single-phase motor :
A type of motor with low horsepower that operates on 120 or 240 volts. Single-phase motors are often used in residential appliances like washing machines and air conditioners.
* slip :
The difference between a motor's synchronous speed and its speed at full load. Percent slip is a way to measure the speed performance of an induction motor.
* slip ring :
A conductive device attached to the end of a generator rotor that conducts current to the brushes. Slips rings are also used in AC wound rotor motors.
* split-phase motor :
A single-phase motor that consists of a running winding, starting winding, and centrifugal switch. The reactance difference in the windings creates separate phases, which produce the rotating magnetic field that starts the rotor.
: squirrel cage rotor :
A type of three-phase AC rotor that is constructed by connecting metal bars together at each end. It is the most common AC rotor type.
* starting winding :
Fine, insulated copper wire in a single-phase motor that receives current in the motor at start-up. When the motor reaches 60-80% of the full load, the starting winding is disconnected and the running winding remains in the circuit.
* stator :
The stationary part of a motor.
* stepped down :
In electricity, a phrase used to describe voltage adjustment. To step down voltage means to decrease voltage.
* stepped up :
In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.
* synchronous motor :
A constant-speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.
* thermal switch :
A type of switch often found in split-phase motors that signals that the motor may overheat
* three-phase motor :
A motor with a continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.
* torque :
A force that produces rotation.
* transform :
To increase or decrease the voltage in a circuit
* wound rotor :
A type of three phase rotor that contains windings and slip rings. This motor type permits control of rotor current by connecting external resistance in series with the rotor windings.

 

[amberleaf]

How to Test & Troubleshoot Electric Motors :

Step (1) Place safety glasses over your eyes. Any time you are repairing an electrical device, safety glasses should be your number one tool. Shut off all electric power to the motor, whether this is turning off a circuit breaker or removing fuses from the disconnect switch.

Step (2) Remove the wiring cover on the motor and set aside the screws so you do not lose them. Read the motor's nameplate data to confirm whether this is a low voltage 115 volt motor, a 230 volt motor, or a 3-phase 230 volt or high voltage 480 volt motor. This will determine the number of power leads the motor has. All single phase 115 volt and 230 volt motors have two wire leads that connect to the power supply. All 3-phase 230 volt and 480 volt motors have three wire leads that connect to the 3-phase power supply.

Step (3) Remove the plastic wire connectors that are connecting to the power supply. You may have to identify the power leads to the wires on the motor if it is a 3-phase motor. This will ensure the rotation will be correct when re-terminating the motor. Turn your volt ohm meter to the ohm setting. The meter should read OL (open lead) or zero ohms. Take one lead and touch it to the case of the motor and test each motor lead. The ohm meter should read OL or zero ohms. If a reading of any ohms is observed you may have a direct short in the motor windings; the motor may be bad. Some motors, especially the 3-phase type, may have a very large resistance reading--in the 20 megaohms range or larger. This may be fine, or this may be a sign that the bearings are going bad as the motor may have deteriorating windings due to excessive heat.

Step (4) Testing single phase motors, whether they are 115 volt or 230 volt, with a capacitor is a little trickier but can still be accomplished. Remove the capacitor from its housing, being careful no to touch the exposed leads. The capacitor is like a battery and stores a high voltage charge. Turn your volt ohm meter to volts and carefully touch to the bare leads of the capacitor. If voltage is read, the capacitor still contains a charge. Holding the leads of the meter to the capacitor should show it discharging, Continue until zero voltage is observed on the meter. Most modern volt ohm meters have a capacitor testing switch on them and it is a simple matter to determine the status of the capacitor. In most cases the capacitor only needs to be replaced on these type of single phase motors.

* Check for blown line fuses or tripped breakers first, if your motor won't start at all. If it has failed while running, allow the motor to cool and then try to reset it.

Heavy duty electrical motors most often consist of split-phase induction motors designed for heavy duty assignments. As split-phase motors use a separate starter winding, these require a capacitor in the starting circuit to provide increased starting power. Failure of split-phase induction motors is often corrected by troubleshooting the capacitor function as described.

Diagnosing Capacitor Malfunction

Step (1) Attempt to start the induction motor. In there is a malfunction, the motor hums but does not start.
Step (2) Rule out malfunction of the centrifugal starter switch by spinning the rotor shaft by hand. If the shaft is frozen the problem is in the switch, and it most be replaced.
Step (3) If the rotor shaft rotates freely by hand, attempt to start the motor. If it starts the switch is either defective or stuck in the closed position, and the motor will stop running. Use electrical contact cleaner to clean the switch. Replace the switch if cleaning fails to correct problem.
Step (4) Rule out a malfunctioning centrifugal switch as above before assuming a failed capacitor function.
Once the switch has been ruled out, a motor that continues to hum ( has current ) but is too weak or otherwise fails to start may be the result of a short or open circuit in the capacitor.
Troubleshooting the Capacitor :
Step (1) Locate the capacitor, which is usually mounted on the side of the induction engine.
Step (2) Remove electrical wires from the two male contacts on the front of the capacitor.
Step (3) Set the volt ohmmeter to the 100 scale and connect the positive and negative leads from the volt ohmmeter to the two contacts of the capacitor.
Step (4) Observe the meter reading. If the needle jumps immediately to zero ohms and gradually drifts back to a high ohm reading, the capacitor is functional and is not the problem.
Step (5) A meter reading that registers steady zero ohms or steady high ohms indicates the capacitor is malfunctioning and should be replaced.
Step (6) Double check meter results by reversing meter leads to the capacitor and re-checking the readings.

Tips : One indicator of an open circuit in a faulty capacitor is high frequency interference in nearby radios when the motor is use.

 

[amberleaf]

Flickering fluorescent tubes can cause the ballast to overheat and fail prematurely! They can even cause a starter to burn out! Don't wait too long to fix the problem or you may end up with a bigger repair!

look at the tube! If either tube appears to be very dark near either end the tube is defective or close to failure.

* An electrical short is often called a short circuit. It is a path for electrical current to flow that is the result of a defect or a breakdown of the electrical circuit. Because it's a clear path for electrical current, electrical shorts can be found by using an ohmmeter, which measures resistance, which is measured in units called ohms, to electrical current. A typical electrical short will have a very low resistance, usually less than a few ohms. By using an ohmmeter and a few simple troubleshooting techniques, you can identify electrical shorts.

 

[amberleaf]

Electric Wiring :

If we connect a voltmeter between a live part ( e.g. the Line Conductor of a socket outlet ) and earth , we read 230V ;
The conductor is at 230V and the earth at Zero . The Earth provides a path to complete the circuit , We would measure nothing at all if we connected our voltmeter , say the positive 12v terminal of a car battery and Earth , as in this case the Earth plays no part in any circuit ,

Colours of indicator lights and their meanings

Colour : RED : Emergency Explanation : Warning of potential danger or a situation which requires immediate action
Typical application : • Failure of pressure in the lubricating system , • Temperature outside specified (safe) limits , • Essential equipment stopped by action of a protective device ,
Colour : Yellow : Meaning Abnormal condition , Explanation Impending critical condition , • Temperature (or pressure) different from normal level , • Overload, which is permissible for a limited time ,
• Reset ,
Colour : Green : Meaning : Normal Explanation : Indication of safe operating conditions or authorization to proceed, clear way Typical application : • Cooling liquid circulating • Automatic tank control switched on • Machine ready to be started
Colour : Blue : Meaning : Enforced action : Explanation : Operator action essential Typical application : • Remove obstacle • Switch over to Advance ,
Colour : White : Meaning : No specific meaning , Explanation : Every meaning: may be used whenever doubt exists about the applicability of the colours RED, YELLOW or GREEN; or as confirmation

Crimp terminals :

Crimp terminals are used for connecting wire by means of a screw joint to: bus-bar, switchgear housing, electric device and apparatus, etc. Terminals with rated sizes up to 0,5 - 6 mm² are designed in principle for a particular wire cross-sections, e.g. 6 mm² terminal can be used for the wires with a cross-section of 4 to 6 [mm²]. Terminal with a cross-section over 6 mm² can be used only for defined wire cross-section. Crimp terminals can only be used on stranded wire and cannot be used on solid cable.←←

Here are some of the more popular crimp terminals : Ring terminals , Fork terminals , Blade terminals , Fully insulated Female push-ons , Butt connectors , Butt connectors are used to join two wires together. You can also find terminals such as pins, male tabs, piggy back, male and female bullets.
Do not forget that the color is also important. Each color represents a different size of crimp terminal. Red ones should be used for the wires with a cross-section of 0,75mm2 to 1,5mm2. Blue ones for the wires from 1,5mm2 to 2,5mm2, and yellow terminals are for the wires with a cross-section of 4mm2 to 6mm2.

RED : wire size : 0,5 - 1,5mm BLUE : wire size 1,5 - 2,5mm YELLOW : 4 - 6mm

Colours of push-buttons and their meanings :
Colour RED : Meaning : Emergency ,
Typical application : * Emergency stop * Fire fighting

Colour YELLOW :
Meaning : abnormal conditions
Typical application : Intervention, to suppress abnormal conditions or to avoid unwanted changes

Colour GREEN :
Meaning : Normal ,
Typical application : Start from safe condition

Colour BLUE :
Meaning : Enforced action ,
Typical application : Resetting function

Colour WHITE :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF

Colour Gray :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF


Colour BLACK :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF

Insulation resistance : Pat ;
Insulation resistance is normally checked by applying 500V dc between both live conductors (line and neutral) connected together and protective earth when testing a Class I appliance

Competence of the inspector
A final consideration when carrying out inspection and tests is the competence of the inspector. Any person undertaking these duties must be skilled and experienced and have sufficient knowledge of the type of installation. It is the responsibility of the inspector to:

* ensure no danger occurs to people, property and livestock
* confirm that test and inspection results comply with the requirements of BS 7671 and the designer’s requirements
* express an opinion as to the condition of the installation and recommend remedial works
* make immediate recommendations, in the event of a dangerous situation, to the client to isolate the defective part.

The inspection process

In new installations, inspection should be carried out progressively as the installation is installed and must be done before it is energised. As far as is reasonably practicable, an initial inspection should be carried out to verify that:

* all equipment and material is of the correct type and complies with applicable British Standards or acceptable equivalents
* all parts of the fixed installation are correctly selected and erected no part of the fixed installation is visibly damaged or otherwise defective
* the equipment and materials used are suitable for the installation relative to the environmental conditions.

 

[amberleaf]

EXTENT AND FREQUENCY OF INSPECTION & TESTING

WHAT IS REQUIRED TO BE INSPECTED AND TESTED ? All types of mains powered electrical portable, moveable, hand-held, stationary, fixed, equipment for 'building-in', I.T. equipment and extension leads are required to be regularly inspected and tested.

It should be noted that provision of new appliance does not exempt the need for formal Inspection and Testing. Manufacturer's warranties only provide for repair or replacement of a faulty device, they do not guarantee that a new device is electrically safe.
Equipment Types :

* Portable Appliance
An appliance of less than 18gm in mass that is intended to be moved while in operation or an appliance which can easily be moved from one place to another, e.g.;- Toaster, Food Mixer, Vacuum Cleaner, Fan Heater

* Movable Equipment (sometimes called transportable)
This is equipment that is either:
18Kg or less in mass and not fixed, e.g. Electric Fire, or equipment with wheels, castors or other means to facilitate movement by the operator as required to perform its intended use, e.g. Air Conditioning Unit.
* Hand-Held Appliances or Equipment
This is portable equipment intended to be held in the hand during normal use e.g.
Hair Dryer, Power Drill, Soldering Iron, Angle Grinder

* Stationary Equipment or Appliances
This equipment has a mass exceeding 18Kg and is not provided with a carrying handle e.g. Refrigerator, Washing Machine, Dishwasher

* Fixed Equipment/Appliances
This is equipment or an appliance which is fastened to a support or otherwise secured in a specified location e.g. Convector Heater, Water Heater, Heated Towel Rail, Production Machinery, Fixed Tools

* Appliances/Equipment for Building-In
This equipment is intended to be installed in a prepared recess such as a cupboard or similar. In general, equipment for building-in does not does not have an enclosure on all sides because on one or more of the sides additional protection against electric shock is provided by the surroundings e.g. Built-In Cooker, Built-In Dishwasher

* Information Technology Equipment (Business Equipment)
Information technology equipment includes electrical business equipment such as computers and mains powered telecommunications equipment and other equipment for general business use e.g. Mail Processing Machines, Electric Plotters, Trimmers, PCs, VDUs, Data Terminal Equipment, Telephones, Printers, Photo-Copiers, Power Packs

* Extension Leads, RCD Extension Leads & RCD Adaptors
The use of extension leads other than for temporary power supplies should be avoided were possible. RCDs are required to be checked for operation.

* The Environment - equipment installed in a benign environment will suffer less damage than equipment used in an arduous environment.

* The Equipment's Construction - Class 1 equipment is dependant upon the connection with earth of the fixed installation.

* The Equipment Type - Hand-held appliances are more likely to be damaged than fixed appliances. If they are Class I appliances then the risk of danger is increased as safety is dependant upon the continuity of the protective (earth) conductor from the plug to the appliance. The initial frequency of inspection and testing should comply with the Institution of Electrical Engineer’s Code of Practice for the In-Service Inspection and Testing of Electrical equipment.

Insulation resistance test

insulation resistance test being conducted on a twin and earth cable between the line and cpc at the distribution board end of the cable.
The reading obtained should be greater than 100 MΩ, indicating that the insulation resistance is satisfactory and that the supply is safe to put on. But what would the instrument indicate in the situation ?

In the situation an insulation resistance test is again being conducted between line and cpc. However, this time a nail has penetrated the sheath of the cable, breaking the cpc and touching the line conductor .When the test is done the instrument may read greater than 100 MΩ, indicating that the insulation resistance is acceptable and that it is safe to connect the supply. However, we can clearly see that it is not. Beyond the break in the cpc, the line and cpc are connected. If the supply was now connected to the cable we would have a potentially lethal situation, as all the metal work connected to the cpc will become live. Automatic disconnection will not take place as the break in the cpc means there is no longer a return path. The metalwork will remain live until someone touches it – which could result in a fatal electric shock In this case,
** if we had conducted a Continuity Test of the cpc before the insulation resistance test, we would have identified that the cpc was broken. Action could then have been taken to remedy the situation

Electrical Terms :

CCT - Circuit
CCU - Cooker Control Unit
CPC - Circuit Protective Conductor
CU - Consumer Unit
The CNE conductor (combined neutral and earth) PEN
EEBAD - Earthed Equipotential Bonding And Automatic Disconnection Of Supply ( Old ) must be replace now ,
ELV - Extra Low Voltage = Below 50V AC \ 120V Ripple Free DC
FCU - Fused Connection Unit
FELV - Functional Extra Low Voltage
HBC - High Breaking Capacity
HRC - High Rupturing Capacity
HV - High Voltage
LV - Low Voltage = 50V - 1000V AC \ 1500V Ripple Free DC
MCB - Miniature Circuit Breaker
MCCB - Moulded Case Circuit Breaker
MD - Maximum Demand
MICC - Mineral Insulated Copper Cable aka Pyro
PAT - Portable Appliance Testing
PELV - Protected Extra Low Voltage
PEN - Protective Earthed Neutral
PFC - Prospective Fault Current
PME - Protective Multiple Earthing
PSCC - Prospective Short Circuit Current
PVC - Poly Vinyl Chloride
RCBO - Residual Current Breaker With Integral Overload Protection
RCCB - Residual Current Circuit Breaker
RCD - Residual Current Device
SELV - Separated Extra Low Voltage
SRCBO's - Socket Outlet Incorporating RCBO's
SWA - Steel Wire Armour (Cable)
UPS - Uninterruptible Power Supply
VD - Voltage Drop

A - Amp
W - Watt
V - Volt
R - Resistance
Z - Impedance
mA - milliampere
mV - millivolt
kW - Kilowatt
kV – Kilovolt

 

[amberleaf]

Alternating current circuit calculations :

Impedance ,

In DC, circuits ,the current is limited by résistance . In AC ,circuits , the current is limited by Impedance ( Z ) Résistance & Impedance are measured in Ohms ,

For this calculation , Ohms law is used and ( Z ) is substituted for ( R ) U – Z = I or voltage ( U ) ÷ impedance ( Ohms ) = Current ( Amperes )
* the voltage applied to a circuit with an impedance of 6Ω , is 200 volts , calculate the current in the circuit ,
U – Z = I ( 200 ÷ 6 = 33.33A )
* the current in a 230V single–phase motor is 7.6A calculate the impedance of the circuit , U – I = Z ( 230 ÷ 7.6 = 30.26Ω )
* a discharge lamp has an impedance of 265Ω and the current drawn by the lamp is 0.4A , calculate the voltage
Z x I = U ( 265 x 0.4 = 106 volts )
* the current through an impedance of 32Ω is 8A , calculate the voltage drop across the impedance U = I x Z = 8 x 32 = 256v
* the current through an electric motor is 6.8A at 230V , calculate the impedance of the motor , U = I x Z
( transpose for Z ) Z = U – I ( 230 ÷ 6.8 = 33.82Ω )
* an AC . coil has an impedance of 430Ω calculate the voltage if the coil draws a current of 0.93A
U = I x Z ( U = I x Z 0.93 x 430 = 400V )

* a mercury vapour lamp take 2.34A when the mains voltage is 237V calculate the impedance of the lamp circuit ?
* an inductor has an impedance of 365Ω how much current will flow when it is connected to a 400V ac supply ?
* a coil of wire passes a current of 55A when connected to a 120V dc supply but only 24.5A when connected to a 110V ac supply calculate (a) the résistance of the coil (b) its impedance ,

Test to measure the impedance of an earth fault loop were made in accordance with BS-7671 and the results for five different installations are given below , for each case calculate the value of the loop impedance ,

(a) test voltage ac ( V ) 9.25 : Current ( A ) 19.6 (b) test voltage ac ( V ) 12.6 : Current ( A ) 3.29
(c) test voltage ac ( V ) 7.65 : Current ( A ) 23.8 (d) test voltage ac ( V ) 14.2 : Current ( A ) 1.09 (e) test voltage ac ( V ) 8.72 : Current ( A ) 21.1

* the choke in a certain fluorescent-fitting causes a voltage drop of 150V when the current through it is 1.78A , calculate the impedance of the choke ,
* the alternating voltage applied to a circuit is 230V and the current flowing is 0.125A , the impedance of the circuit is ,
(a) 5.4Ω (b) 1840Ω (c) 3.5Ω (d) 184Ω ,
* an alternating current of 2.4A flowing in a circuit of impedance 0.18Ω produces a voltage drop of
(a) 0.075V (b) 13.3V (c) 0.432V (d) 4.32V ,
* when an alternating e.m.f of 150V is applied to a circuit of impedance 265Ω , the current is ,
(a) 39 750A (b) 1.77A (c) 5.66A (d) 0.566A

We will assume that the résistance of the circuits is so low that it may be ignored and that the only opposition to the flow of current is that caused by the inductive reactance ,
The formula for inductive reactance , ( is XL = 2nfL ( answer in ohms )
Where L is the inductance of the circuit or coil of wire and is stated in henrys ( H ) f is the frequency of the supply in hertz (Hz )
* calculate the inductive reactance of a coil which has an inductance of 0.03 henrys when connected to a 50Hz supply
( XL = 2nfL ( 2 x 3 . 142 x 50 x 0.03 = 9.42Ω
* calculate the inductive reactance of a coil when connected to a 60Hz supply , XL 2nfL ( = 2 x 3. 142 x 60 x 0.03 = 11.31Ω )
It can be seen from this calculation that the frequency increases the inductive reactance will also increase ,

 

[amberleaf]

Working knowledge :

What we call "Electricity" is actually made up of three parts.

Real Power (Kw, Mw),
Apparent Power (Kva),
Reactive Power (Kvar).
These 3 parts form the "Power Triangle"

Real Power (Kw) is the part of the triangle which results in real work done, in the form of heat energy.

Apparent Power is that portion of the power triangle that we actually measure.

And then....there is Reactive Power....which serves no real function at all.

The phase angle between Real Power and Apparent Power in the power triangle is identified as the angle "q" which is the Greek letter "THETA". The size, in degrees, of that angle determines the size of the Reactive Power leg of the triangle. The cosine of that angle is called Power factor or pf and the value of the pf is inversely proportional to the amount of reactive power you are generating. What this means is that the smaller the angle q, the less Reactive Power you are making and the greater your Power Factor is.

Electrical

A = Ampere
V = Volt
W = Watt
Ω = Ohm
F = Farad

Power / Energy

HP = horsepower
W = watt
kW = kilowatt
kWh = kilowatt-hours

I = Current (ampere)
U = Voltage (volt)
R = Resistance (ohm)

Electrical power

P = U x I x PF / 1000
P =Power in kW (1-phase)
PF = Power factor

P = U x I x PF x √2 / 1000
P =Power in kW (2-phase)

P = U x I x PF x √3 / 1000
P =Power in kW (3-phase)

Conversion factors

Power
1 hp = 0,736 kW 1 kW = 1,36 hp
1 hp = 0,746 kW (UK,US) 1 kW = 1,34 hp (UK;US)
1 kcal/h = 1,16 W 1 W = 0,860 kcal/h

Energy
1 kpm = 9,80665 J 1 J = 0,102 kpm
1 cal = 4,1868 J 1 J = 0,239 cal
1 kWh = 3,6 MJ 1 MJ = 0,278 kWh

Mass
1 lb = 0,454 kg 1 kg = 2,20 lb
Area
1 acre = 0,405 ha 1 ha = 2,471 acre

Length
1 mile = 1,609344 km 1 km = 0,621 mile
1 yd = 0,9144 m 1 m = 1,09 yd
1 ft = 0,3048 m 1 m = 3,28 ft
1 in = 25,4 mm 1 mm = 0,039 in

 

[amberleaf]

Insulation Résistance Test :

Insulation résistance is normally checked by applying 500V dc
Between both Live Conductors ( Line & Neutral ) and Protective Earth when Testing a Class 1 Appliance .

Mathematical :

˂ Less than .
≤ Less than or Equal to .
˃ More than .
≥ More than or Equal to .

Inspection checklists :

To ensure that all the requirements of the Regulations have been met, inspection checklists should be drawn up and used as appropriate to the type of installation being inspected. Examples of suitable checklists are given in which follows.

Switchgear ( tick if satisfactory )

All switchgear is suitable for the purpose intended .
Meets requirements of the appropriate BS EN standards .
Securely fixed and suitably labelled .
Suitable glands and gland plates used (526.1) .
Correctly earthed .
Conditions likely to be encountered taken account of, i.e. suitable for the environment .
Correct IP rating .
Suitable as means of isolation .
Complies with the requirements for locations containing a bath or shower .
Need for isolation, mechanical maintenance, emergency and functional switching met .
Fireman switch provided, where required .
Switchgear suitably coloured, where necessary .

Lighting controls ( tick if satisfactory )

Light switches comply with appropriate British Standard .
Switches suitably located .
Single-pole switches connected in phase conductor only .
Correct colour-coding of conductors .
Correct earthing of metal switch plates .
Switches out of reach of a person using bath or shower .
Switches for inductive circuits (discharge lamps) de-rated as necessary .
Switches labelled to indicate purpose where this is not obvious .
All switches of adequate current rating .
All controls suitable for their associated luminaire .

Lighting points ( tick if satisfactory )

All lighting points correctly terminated in suitable accessory or fitting .
Ceiling roses comply with appropriate British Standard .
No more than one flexible cord unless designed for multiple pendants .
Devices provided for supporting flex used correctly .
All switch wires identified .
Holes in ceiling above ceiling rose made good to prevent spread of fire .
Ceiling roses not connected to supply exceeding 230V .
Flexible cords suitable for the mass suspended .
Lamp holders comply with appropriate British Standard .
Luminaire couplers comply with appropriate British Standard .

Conduits ( general ) ( tick if satisfactory )

All inspection fittings accessible .
Maximum number of cables not exceeded .
Solid elbows used only as permitted .
Conduit ends reamed and bushed .
Adequate number of boxes .
All unused entries blanked off .
Lowest point provided with drainage holes where required .
Correct radius of bends to prevent damage to cables .
Joints and scratches in metal conduit protected by painting .
Securely fixed covers in place adequate protection against mechanical damage .

Wiring accessories ( general requirements) (tick if satisfactory )

All accessories comply with the appropriate British Standard
Boxes and other enclosures securely fastened
Metal boxes and enclosures correctly earthed
Flush boxes not projecting above surface of wall
No sharp edges which could cause damage to cable insulation
Non-sheathed cables not exposed outside box or enclosure
Conductors correctly identified
Bare protective conductors sleeved green and yellow
All terminals tight and contain all strands of stranded conductor
Cord grips correctly used to prevent strain on terminals
All accessories of adequate current rating
Accessories suitable for all conditions likely to be encountered
Complies with the requirements for locations containing a bath or shower
Cooker control unit sited to one side and low enough for accessibility and to prevent trailing flexes
across the radiant plates
Cable to cooker fixed to prevent strain on connections

Socket outlet ( tick if satisfactory )

Complies with appropriate British Standard and is shuttered for household and similar installations
Mounting height above floor or working surface is suitable
All sockets have correct polarity
Sockets not installed in bath or shower zones unless they are shaver-type socket or SELV
Sockets not within 3m of zone 1
Sockets controlled by a switch if the supply is direct current
Sockets protected where floor mounted
Circuit protective conductor connected directly to the earthing terminal of the socket outlet on a sheathed wiring installation
Earthing tail provided from the earthed metal box to the earthing terminal of the socket outlet
Socket outlets not used to supply a water heater with uninsulated elements

Rigid metal conduits (tick if satisfactory)
Complies to the appropriate British standard
Connected to the main earth terminal
Line and neutral cables contained within the same conduit
Conduits suitable for damp and corrosive situations
Maximum span between buildings without intermediate support

Rigid non-metallic conduits (tick if satisfactory)
Complies with the appropriate British Standard
Ambient and working temperature within permitted limits
Provision for expansion and contraction
Boxes and fixings suitable for mass of luminaire suspended at expected temperatures

Flexible metal conduit (tick if satisfactory)
Complies with the appropriate British Standard
Separate protective conductor provided
Adequately supported and terminated

Trunking (tick if satisfactory)
Complies to the appropriate British Standard
Securely fixed and adequately protected against mechanical damage
Selected, erected and rooted so that no damage is caused by ingress of water
Proximity to non-electrical services
Internal sealing provided where necessary
Hole surrounding trunking made good
Band 1 circuits partitioned from band 2 circuits, or insulated for the highest voltage present .
Circuits partitioned from band one circuits, or wired in mineral-insulated and sheathed cable .
Common outlets for band 1 and band 2 circuits provided with screens, barriers or partitions .
Cables supported for vertical runs

Metal trunking (tick if satisfactory )
Line and neutral cables contained in the same metal trunking
Protected against damp corrosion
Earthed
Joints mechanically sound, and of adequate earth continuity with links fitted

Plant , Equipment & component failure :

It is said that nothing lasts forever and this is certainly true of electrical equipment there will be some faults that you will attend that will be the result of a breakdown simply caused by wear & tear , although it must be said that planned maintenenance systems and regular testing and inspections can extend the life of equipment , some common failures on installations and plant are :
* switches not operating – due to age .
* motors not running – new brushes required .
* lighting not working – lamps life expired .
* fluorescent luminaire not working – new lamp or starter needed .
* outside PIR not switching – ingress of water causing failure.
* corridor socket outlet not working due to poor contacts created by excessive use / age .

The intention of the measure is to phase out less efficient lamps in favour of products with greater energy efficiency. A brief description of the lamps affected by the measure follows below along with a summary of main characteristics

A. Incandescent lamps (General Lighting Service (GLS))
These lamps are the traditional filament lamps which have been in domestic use for decades and provide a bright light source when made with transparent glass. They are very low efficiency lamps compared with other lamps (CFLs in particular) but are generally available in good quality, and provide good performance.

B. Conventional halogen lamps (Halo conv)
Standard halogen lamps consume at best, 15% less energy than GLS lamps for the same light output. Many of these lamps are low voltage lamps which are more efficient that mains voltageones but which require a transformer either in the luminaire or in the lamp itself. They provide good quality light.

C. Halogen lamps with xenon filling (C-class)
These are recent technology lamps with xenon filling and will use approximately 25% less energy for the same light output as GLS lamps. These lamps come in two types, one which is placed in glass bulbs, shaped like incandescent lamps, which are compatible with existing luminaries (retro C), and halogen socket c type lamps which can only be used in special halogen sockets (halosocket C). Lamps provide good quality light and performance.

D. Halogen lamps with infrared coating (B-class)
These lamps are new technology, with an application of infrared coating to the wall of the halogen lamp capsule making the lamp considerably more efficient. However, this is only possible with low voltage lamps and therefore a transformer is required. Currently only one manufacturer produces these lamps with a fitting so that they can fit traditional sockets. Due to heat issues, these are only available up to the equivalent of 60W GLS bulbs. They provide a bright light source and good performance and are estimated to provide 45% energy savings over GLS lamps

E. Compact fluorescent lamps (CFLs)
These include an integrated ballast, fit into existing GLS sockets, and are produced with both bare tubes and also with a traditional bulb-shaped cover. They have a long lifetime and vary in their energy efficiency, being estimated to use between 20-35% of energy of that needed for GLS lamps. CFLs are sometimes criticised by consumers resulting from lingering perceptions over poor light quality and it is recognised that long periods of close-up use can have adverse effects on those with pre-existing photo-sensitive conditions.

 

[pipster1973]

thanks very much this has helped me no endl